Precise mechanisms of synthesis and secretion of PRL, FSH and LH are still poorly understood. Only monitoring serum or pituitary levels of gonadotropins will not give a complete understanding of their synthesis or secretion. Since gonadotropes comprise only 15% of the total pituitary population, incorporation of radiolabeled amino acids into newly synthesized protein will not give a very accurate measurement of newly synthesized gonadotropins. In order to more accurately study synthesis and release of FSH, LH and PRL, quantitative electronmicroscopy (morphometry) will be used and correlated with pituitary and serum levels of these hormones in different physiological conditions. Morphometrical methods have not been used extensively in endocrine tissues therefore they must first be validated for use in the pituitary. The morphometrical procedure has been devised an its validity tested in mammotropes during the rat estrous cycle. Such an approach appears very promising and preliminary work showed that changes in mitochondria, endoplasmic reticulum Golgi complexes and secretory granules preceded the peak in pituitary and serum PRL during proestrus of the estrous cycle. Within a 12 hour period these organelles rose up to 150% in volume but regressed hours after the peak. The studies outlined in the first objective will further validate the morphometric method. In the second objective the validity of the morphometric method will be established using a castrate female rat model developed in our laboratory in which large and predictable changes in gonadotropin synthesis and secretion occur over a short period of time. Once the method has been standardized for gonadotrope morphology it will be used to determine changes in these cells during the estrous cycle. These studies will provide new knowledge of synthesis and secretion of FSH, LH and PRL which may be of importance in understanding their control mechanisms and new parameters susceptible to intervention.